Gene expression systems in Drosophila: a synthesis of time and space.

Until recently, ectopic gene expression in Drosophila was largely accomplished through the use of the heat-shock promoter, which provides the experimenter with temporal control over transgene induction, or the GAL4-UAS system, which provides the experimenter with spatial control over transgene expression. But significant advances have now been made in combining the attributes of temporal and spatial control over gene expression into a single system. In this article, we review the progress on the development and implementation of several gene expression systems that offer control in time and space. These include systems employing the yeast FLP recombinase gene and FRT sites (FLP and/or FRT), tetracycline-responsive transcription factors (Tet-On and Tet-Off), steroid hormone responsive transcription factors (GeneSwitch and ER-GAL4) and temperature-sensitive repressors of the classical GAL4-UAS system (TARGET).